Line data    Source code

       1             : // Copyright 2018 the V8 project authors. All rights reserved.
       2             : // Use of this source code is governed by a BSD-style license that can be
       3             : // found in the LICENSE file.
       4             : 
       5             : #ifndef V8_BASE_SMALL_VECTOR_H_
       6             : #define V8_BASE_SMALL_VECTOR_H_
       7             : 
       8             : #include <type_traits>
       9             : 
      10             : #include "src/base/bits.h"
      11             : #include "src/base/macros.h"
      12             : 
      13             : namespace v8 {
      14             : namespace base {
      15             : 
      16             : // Minimal SmallVector implementation. Uses inline storage first, switches to
      17             : // malloc when it overflows.
      18             : template <typename T, size_t kInlineSize>
      19             : class SmallVector {
      20             :   // Currently only support trivially copyable and trivially destructible data
      21             :   // types, as it uses memcpy to copy elements and never calls destructors.
      22             :   ASSERT_TRIVIALLY_COPYABLE(T);
      23             :   STATIC_ASSERT(std::is_trivially_destructible<T>::value);
      24             : 
      25             :  public:
      26     3734087 :   SmallVector() = default;
      27             :   SmallVector(const SmallVector& other) V8_NOEXCEPT { *this = other; }
      28      346196 :   SmallVector(SmallVector&& other) V8_NOEXCEPT { *this = std::move(other); }
      29             : 
      30             :   ~SmallVector() {
      31     2318555 :     if (is_big()) free(begin_);
      32             :   }
      33             : 
      34      440049 :   SmallVector& operator=(const SmallVector& other) V8_NOEXCEPT {
      35      146683 :     if (this == &other) return *this;
      36             :     size_t other_size = other.size();
      37      146683 :     if (capacity() < other_size) {
      38             :       // Create large-enough heap-allocated storage.
      39          27 :       if (is_big()) free(begin_);
      40          27 :       begin_ = reinterpret_cast<T*>(malloc(sizeof(T) * other_size));
      41          27 :       end_of_storage_ = begin_ + other_size;
      42             :     }
      43      146683 :     memcpy(begin_, other.begin_, sizeof(T) * other_size);
      44      146683 :     end_ = begin_ + other_size;
      45      146683 :     return *this;
      46             :   }
      47             : 
      48      346197 :   SmallVector& operator=(SmallVector&& other) V8_NOEXCEPT {
      49      173095 :     if (this == &other) return *this;
      50      173102 :     if (other.is_big()) {
      51           0 :       if (is_big()) free(begin_);
      52           0 :       begin_ = other.begin_;
      53           0 :       end_ = other.end_;
      54           0 :       end_of_storage_ = other.end_of_storage_;
      55             :       other.reset();
      56             :     } else {
      57             :       DCHECK_GE(capacity(), other.size());  // Sanity check.
      58             :       size_t other_size = other.size();
      59      173102 :       memcpy(begin_, other.begin_, sizeof(T) * other_size);
      60      173102 :       end_ = begin_ + other_size;
      61             :     }
      62             :     return *this;
      63             :   }
      64             : 
      65             :   T* data() const { return begin_; }
      66             :   T* begin() const { return begin_; }
      67             :   T* end() const { return end_; }
      68     2726549 :   size_t size() const { return end_ - begin_; }
      69             :   bool empty() const { return end_ == begin_; }
      70      305885 :   size_t capacity() const { return end_of_storage_ - begin_; }
      71             : 
      72             :   T& back() {
      73             :     DCHECK_NE(0, size());
      74             :     return end_[-1];
      75             :   }
      76             : 
      77             :   T& operator[](size_t index) {
      78             :     DCHECK_GT(size(), index);
      79     7269596 :     return begin_[index];
      80             :   }
      81             : 
      82             :   const T& operator[](size_t index) const {
      83             :     DCHECK_GT(size(), index);
      84       70634 :     return begin_[index];
      85             :   }
      86             : 
      87             :   template <typename... Args>
      88     4334414 :   void emplace_back(Args&&... args) {
      89     4334414 :     if (V8_UNLIKELY(end_ == end_of_storage_)) Grow();
      90     4334491 :     new (end_) T(std::forward<Args>(args)...);
      91     4334491 :     ++end_;
      92     4334491 :   }
      93             : 
      94             :   void pop_back(size_t count = 1) {
      95             :     DCHECK_GE(size(), count);
      96     2801694 :     end_ -= count;
      97             :   }
      98             : 
      99      138914 :   void resize_no_init(size_t new_size) {
     100             :     // Resizing without initialization is safe if T is trivially copyable.
     101             :     ASSERT_TRIVIALLY_COPYABLE(T);
     102      138914 :     if (new_size > capacity()) Grow(new_size);
     103      138914 :     end_ = begin_ + new_size;
     104      138914 :   }
     105             : 
     106             :   // Clear without freeing any storage.
     107             :   void clear() { end_ = begin_; }
     108             : 
     109             :   // Clear and go back to inline storage.
     110             :   void reset() {
     111           0 :     begin_ = inline_storage_begin();
     112           0 :     end_ = begin_;
     113           0 :     end_of_storage_ = begin_ + kInlineSize;
     114             :   }
     115             : 
     116             :  private:
     117     1588587 :   T* begin_ = inline_storage_begin();
     118             :   T* end_ = begin_;
     119     1761685 :   T* end_of_storage_ = begin_ + kInlineSize;
     120             :   typename std::aligned_storage<sizeof(T) * kInlineSize, alignof(T)>::type
     121             :       inline_storage_;
     122             : 
     123       40576 :   void Grow(size_t min_capacity = 0) {
     124       20288 :     size_t in_use = end_ - begin_;
     125             :     size_t new_capacity =
     126       60864 :         base::bits::RoundUpToPowerOfTwo(std::max(min_capacity, 2 * capacity()));
     127       20288 :     T* new_storage = reinterpret_cast<T*>(malloc(sizeof(T) * new_capacity));
     128       20288 :     memcpy(new_storage, begin_, sizeof(T) * in_use);
     129       20288 :     if (is_big()) free(begin_);
     130       20288 :     begin_ = new_storage;
     131       20288 :     end_ = new_storage + in_use;
     132       20288 :     end_of_storage_ = new_storage + new_capacity;
     133       20288 :   }
     134             : 
     135     2511972 :   bool is_big() const { return begin_ != inline_storage_begin(); }
     136             : 
     137             :   T* inline_storage_begin() { return reinterpret_cast<T*>(&inline_storage_); }
     138             :   const T* inline_storage_begin() const {
     139             :     return reinterpret_cast<const T*>(&inline_storage_);
     140             :   }
     141             : };
     142             : 
     143             : }  // namespace base
     144             : }  // namespace v8
     145             : 
     146             : #endif  // V8_BASE_SMALL_VECTOR_H_